Depending upon the threat level, a fast mover "cigarette boat" that is on a collision course and doesn't identify itself on VHF Ch 16 could be fired upon, as well, even in US waters. Just a heads up
We actually ran over a sailboat in San Diego harbor once. He took us to court. He figured that being a sailboat gave him right of way, even though we were restricted in our ability to manuever. The judge awarded him a $700 judgement to pay us for the paint he scratched off the ship.